The present invention relates to a transmission for a self-propelled machine, such as a self-propelled lawn mower, as well as a self-propelled machine provided with such a transmission.
The present invention relates more particularly to a transmission of the type comprising an endless belt transmission between a drive pulley mounted on a primary motor shaft constituting, in the case of a lawn mower, the driven shaft that carries the mowing blade of said mower and driven pulley carried by the input shaft of a clutch engaging mechanism whose output shaft is coupled to the wheels of the machine.
A transmission of this type is particularly provided in the European patent application EP 0 717 920. Such a transmission operates perfectly when clutch engagement is of the progressive type. In the contrary case, there is experienced a certain number of jolts with each clutch engagement, jolts which are disagreeable for the driver and which are adapted to lead to accidents. However, such progressive clutch engaging mechanisms are generally complicated and cumbersome.
Another category of transmission is constituted by transmissions incorporating only transmissions without an endless belt. Unclutching such a transmission without a belt is generally carried out by relaxing the belt. However, during use, it happens that the belt in the relaxed condition is maintained continuously in frictional engagement in the throat of the pulley. This friction gives rise on the one hand to premature wear of the belt, and on the other hand to a resistant couple, in particular when the self-propelled machine is driven in reverse. A second drawback of these endless belt transmissions resides in the difficulty of guiding the belt to bring it to the slack condition and then to return it to the stretched position.
Finally, there is known from U.S. Pat. No. 4,907,401 a transmission for a self-propelled machine of the type comprising an endless belt transmission between a driving pulley mounted on a primary motor shaft and a driven pulley carried by the input shaft of a mechanism, generally a speed reducer, with clutch engagement whose output shaft is coupled to the wheels of the machine, the clutch engaging mechanism being a non-progressive clutch engagement with a toothed clutch disposed within a housing, this housing being mounted oscillably about the output shaft of the clutch engaging mechanism in the direction of tension or respectively of relaxation of the endless transmission belt, at least under the action of a control mechanism constituted by a pivoting lever which at least partially projects from the housing, the operation of this lever being subject to a control member of the clutch engaging mechanism so as to give rise, in the first instance, to the passage from the clutch engaged position of the mechanism with clutch engagement and then, in the second instance, the tensioning of the belt to obtain movement of the machine. Such a transmission requires, to obtain a variation of the speed of advance of the machine, the incorporation in the clutch engaging housing of a speed change box. This speed box is controlled by a lever by the operator. The operator must thus act on the one hand on the speed change lever, and on the other hand on the clutch engagement mechanism to obtain advance of the machine with variable speed. Such an embodiment is complex and cumbersome and complicated to use.
An object of the present invention is to provide a transmission for a self-propelled machine whose design permits being perfectly unclutchable in a way so as not to prevent, in the unclutched position, the forward or rearward movement of said machine, this transmission moreover permitting forward movement at variable speed of the machine without having recourse to a speed change box.
Another object of the present invention is to provide a transmission for a self-propelled machine whose design permits a passage to the clutch engaged position which takes place in a progressive manner without jolts, despite the presence of a non-progressive type of clutch engagement.
To this end, the invention has for its object a transmission for a self-propelled machine of the type comprising an endless belt transmission between a driving pulley mounted on a primary motor shaft and a driven pulley carried by the input shaft of a mechanism, generally a speed reducer, with clutch engagement whose output shaft is coupled to the wheels of the machine, the clutch engaging mechanism being a non-progressive toothed clutch engagement disposed within a housing, this housing being mounted swingably about the output shaft of the clutch engaging mechanism in the direction of tension or respectively of relaxation of the belt of the endless transmission, at least under the action of a control mechanism constituted by a pivotal lever which projects at least partially from the housing, the function of this lever being subject to the control member of the clutch engaging mechanism so as to cause, in a first instance, the passage from the clutch engaged position of the clutch engaging mechanism, then, in a second instance, the tensioning of the belt to obtain movement of the machine, characterized in that the movement of the machine is of the variable speed type, the variation of speed being obtained by variation of the tension applied to the belt with the aid of the pivoting lever disposed outside the clutch engaging housing, so as to eliminate any speed change box with multiple ratios, within said housing.
Thanks to this swinging movement of the housing of the clutch engaging mechanism on the output shaft of the clutch engaging mechanism, it is possible to obtain, in a first instance, the passage to the clutch engaged position of the clutch engaging mechanism and then, in a second instance, the tensioning of the endless transmission belt such that the clutch engagement takes place in a progressive manner, the passage to the unclutched position taking place generally in the reverse manner, namely, by oscillation of the housing in a reverse direction to ensure relaxation of the tension, then passage to the unclutched position of the clutch engaging mechanism. The endless transmission is thus used as a second clutching mechanism which renders the first clutching mechanism progressive. This endless transmission is moreover used as a speed change device by simple variation of the tension of the belt controlled by means of the same control mechanism as that controlling clutch engagement. As a result, there is an extreme simplification of the transmission of the machine.
The invention also relates to a self-propelled wheeled machine, particularly a lawn mower, characterized in that it is provided with a transmission of the above type.